1. Field of the Invention
The present invention relates generally to an arrangement for transmitting an electrical voltage derived from solar energy via microwave transmission to a receiving apparatus which is remote from the transmitting apparatus. Particularly the present invention relates to a subarray panel for accomplishing the above while providing a compact, lightweight structure.
2. Description of the Related Art
Solar Power Satellites (SPS) have recently been proposed for collecting solar electrical energy and transmitting same to be received and utilized at remote locations. The collected energy would be transmitted via microwave to, for example, an orbital space station, factory, or a location on earth or another celestial body. For establishing such as system of energy transfer, efficient receiving and transmission elements are required.
One such system of solar energy collection/transmission has been described in the Jul. 4, 1992 issue of the Asahi Newspaper, morning edition 13, page 15. FIG. 4 shows a representation of the solar energy satellite arrangement. Referring to the drawing, an earth launched solar energy collection/transmission satellite 101 is shown. The satellite 101 is adapted to mount a plurality of subarray assemblies to transmit solar energy in a direction from which a micro wave pilot signal, aimed at the satellite from a remote location, is received.
For realizing such an energy transmission arrangement, for guiding an energy transmission wave and phase control of a generated microwave signal, a microwave pilot signal is emitted from a target point and the subarrays of the energy transmission arrangement must be active to transmit electrical energy back in a target direction from which the pilot signal is received. This has been attempted via phased array antennas and a so-called `retrodirective` transmission method.
Referring to FIG. 5, such a retrodirective method as mentioned above will be explained. First, a pilot signal is emitted at a given frequency .omega..sub.i toward the position of the energy transmission arrangement (i.e. a satellite, not shown in the drawing), from a target point A. The pilot signal is received at a plurality of antenna elements (not shown) of the energy transmission arrangement. In response to reception of the pilot signal, the energy transmission arrangement emits an energy transmission wave at a given frequency .omega..sub.t, in the direction of the target point A. At a time t, when the energy transmission wave arrives at the target point A, a distance X.sub.0 is assumed to separate the target point A from a reference point P.sub.0 on the energy transmission arrangement. At this, a phase of the pilot signal in relation to the reference point P.sub.0 may be expressed as: EQU .phi..sub.0 =.omega..sub.i (t.sub.0 -X.sub.0 /C) (1)
wherein C=the speed of light.
In the same way, since a the target point A is separated from a different point, P.sub.1, on the energy transmission arrangement by an distance X.sub.1, a phase of the pilot signal may be expressed as: EQU .phi..sub.1 =.omega..sub.i (t.sub.0 -X.sub.1 /C) (2)
At this, a phase difference between the two points (P.sub.0, P.sub.1), may be expressed as: EQU .PHI..sub.i =.phi.1-.phi.0=-.omega..sub.i r/C (3)
wherein EQU r=X.sub.1 -X.sub.0.
Provisionally, if the transmission wave is emitted at same phase from both points P.sub.0 and P.sub.1, a phase difference in relation to the target point A is present in the frequency .omega..sub.t of the transmission wave. Relating to the condition noted from equation (3) the phase difference of the transmission wave may be expressed as: EQU .PHI..sub.t =-.omega..sub.t r/C (4)
At this, while a phase of the transmission wave from the the two points P.sub.0 and P.sub.1 are similar, a correction for the phase of the point P.sub.1 may be expressed as: EQU .PHI..sub.c =.omega..sub.t r/C (5)
According to this, phase correction for any number of emission points of the energy transmission arrangement may be effected according to the equation (5). Thus, the phase of emissions of the transmission wave from any point of the energy transmission arrangement can be converged at the target point A, the above being based on the general principles of the retrodirective method.
However, according to the above method, in order to implement an effective energy transmission arrangement, it is necessary to provide a pilot signal receiving antenna for each antenna element of the transmission apparatus, consequently the transmission apparatus becomes large and impractically heavy.
Thus it has been required to provide an energy transmission arrangment in which the energy transmission anntenna elements and the pilot signal receiving antennas are logically arranged while allowing the arrangement to be kept compact and light in weight.